I'm trying to deserialize some JSON to various sub-classes using a custom JsonConverter
I followed this almost to the point.
My abstract base-class:
abstract class MenuItem
{
public String Title { get; set; }
public String Contents { get; set; }
public List<MenuItem> Submenus { get; set; }
public String Source { get; set; }
public String SourceType { get; set; }
public abstract void DisplayContents();
}
And my derived JsonConverter
:
class MenuItemConverter : JsonConverter
{
public override bool CanConvert(Type objectType)
{
return typeof(MenuItem).IsAssignableFrom(objectType);
}
public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
{
JObject item = JObject.Load(reader);
switch (item["SourceType"].Value<String>())
{
case SourceType.File: return item.ToObject<Menu.FileMenu>();
case SourceType.Folder: return item.ToObject<Menu.FolderMenu>();
case SourceType.Json: return item.ToObject<Menu.JsonMenu>();
case SourceType.RestGet: return item.ToObject<Menu.RestMenu>();
case SourceType.Rss: return item.ToObject<Menu.RssMenu>();
case SourceType.Text: return item.ToObject<Menu.TextMenu>();
case SourceType.Url: return item.ToObject<Menu.UrlMenu>();
default: throw new ArgumentException("Invalid source type");
}
}
public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
{
throw new NotImplementedException();
}
}
SourceType
is just a static class holding some string constants.
The JSON file is deserialized like this:
JsonConvert.DeserializeObject<MenuItem>(File.ReadAllText(menuPath), new MenuItemConverter());
Now, my issue is that whenever I run the code I get the following error:
An exception of type 'Newtonsoft.Json.JsonSerializationException' occurred in Newtonsoft.Json.dll but was not handled in user code
Additional information: Could not create an instance of type ConsoleMenu.Model.MenuItem. Type is an interface or abstract class and cannot be instantiated. Path 'Submenus[0].Title', line 5, position 21.
The Json file in question looks like this:
{
"Title": "Main Menu",
"Submenus": [
{
"Title": "Submenu 1",
"Contents": "This is an example of the first sub-menu",
"SourceType": "Text"
},
{
"Title": "Submenu 2",
"Contents": "This is the second sub-menu",
"SourceType": "Text"
},
{
"Title": "GitHub System Status",
"Contents": "{"status":"ERROR","body":"If you see this, the data failed to load"}",
"Source": "https://status.github.com/api/last-message.json",
"SourceType": "RestGet"
},
{
"Title": "TF2 Blog RSS",
"Contents": "If you see this message, an error has occurred",
"Source": "http://www.teamfortress.com/rss.xml",
"SourceType": "Rss"
},
{
"Title": "Submenus Test",
"Contents": "Testing the submenu functionality",
"Submenus": [
{
"Title": "Submenu 1",
"Contents": "This is an example of the first sub-menu",
"SourceType": "Text"
},
{
"Title": "Submenu 2",
"Contents": "This is the second sub-menu",
"SourceType": "Text"
}
]
}
],
"SourceType": "Text"
}
It appears to me that it has trouble deserializing the nested objects, how do I get around that?
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